Subterranean heaters have been used to heat subterranean geological formations in oil production, remediation of contaminated soils, accelerating digestion of landfills, thawing of permafrost, gasification of coal, as well as other uses. Some examples of subterranean heater arrangements include placing and operating electrical resistance heaters, microwave electrodes, gas-fired heaters or catalytic heaters in a bore hole of the formation to be heated. Other examples of subterranean heater arrangements include circulating hot gases or liquids through the formation to be heated, whereby the hot gases or liquids have been heated by a burner located on the surface of the earth. While these examples may be effective for heating the subterranean geological formation, they may be energy intensive to operate.
U.S. Pat. Nos. 6,684,948 and 7,182,132 to Savage propose subterranean heaters which use fuel cells as a more energy efficient source of heat. The fuel cells are disposed in a heater housing which is positioned within the bore hole of the formation to be heated. The fuel cells convert chemical energy from a fuel into heat and electricity through a chemical reaction with an oxidizing agent. If the temperature of a fuel cell falls below a predetermined temperature, for example about 680° C. in some types of fuel cells, a temperature gradient and voltage drop may result which can challenge the operability and life of the fuel cell. Fuel cells that are not located at the bottom of the bore hole are subject to heat from fuel cells that are lower in the bore hole due to heat naturally rising upward through the bore hole. This heat from fuel cells that are lower in the bore hole help to keep the fuel cells that are not located at the bottom of the bore hole above the predetermined temperature. However, the fuel cells that are located at the bottom of the bore hole do not receive additional heat, and are consequently subject to additional heat loss which may allow the fuel cells to drop below the predetermined temperature.
What is needed is a heater which minimizes or eliminates one of more of the shortcomings as set forth above.